We aim to study the changes that take place in the output of the motor system and its neural correlates in the brain as humans learn a motor skill with the arm, and describe how the neural and functional representation of the skill changes in the hours after completion of practice. We hypothesize that during these hours, motor memories undergo a process of consolidation. Our principal experimental tool is a robotic system that subjects learn to control with their arm. We will perform psychophysical and neuroimaging experiments coupled with computational modeling to pursue the following objectives: To understand, using a mathematical model, the changes that take place in the motor output as reaching movements are made in a novel force field; To describe the time course of changes in functional properties of motor memory in the hours after completion of practice; To describe the neural correlates of motor memory consolidation through functional imaging; To ask whether the time- dependent functional properties associated with motor memory are intact in amnesia; To better understand the role of the cerebellum and the striatum in learning of reaching movements by studying motor learning in patients with cerebellar disease and Huntington's Disease. With a better understanding of how the normal brain learns a new motor skills and how time influences its representation, we will better understand motor learning and rehabilitation processes in the damaged brain.